Topic: [ANN] [PPC] PPCoin Released! - First Long-Term Energy-Efficient Crypto-Currency - page 138. (Read 684454 times)

Most likely you have bitcoind already running so you have to set rpcport

Actually a large stash of coins is not even necessary to perform double-spends: you can get extra coin-days-destroyed for your block by paying people to send you their send-to-self transactions privately. As proof-of-stake based mining earns 1% per year, you can pay like 2% per year to make it profitable for them.

Once you have access to transactions which consume a lot of coin-days (relatively to normal spending activity) you can add them to your block and cause a large reorg.

So, basically, what is required is enough hash-power to mine block once in a while, say, once in a hour. And double-spend is pretty much guaranteed.

I've got a pool setup if anyone wants to help test it, create an account @ http://46.166.138.142/

It doesn't matter that it's rare. You can get access to a steady flow of double-spend transactions via a kickback mechanism:

You, a wealthy hacker, would implement a "ppcoin-double-spend-edition" client. It works exactly like a regular client, except there is an additional "double spend lottery" button. When user clicks that button client creates a double-spend transaction for a recent user's transaction and it submits this transaction to you.

This double spend txn will spend 90% of input to user and 10% as a kickback to you.

Now I assume that this client will get popular since users have a chance to buy products for 10% of their cost.

If this client is popular, you get a constant stream of double-spend transactions with kickbacks to you.

You include these double-spend transactions into your proof-of-stake blocks, aiming to trigger a reorg. If you successfully mine it and reorg is successful, you earn kickbacks. If reorg doesn't work, you lose nothing since your coin-days are not consumed and you can try again.

Alternatively, you can use proof-of-work and send-to-self to increase coin-days consumed in your transaction. Quote from the ppcoin paper:


Apparently, it doesn't matter whether coin-days are consumed in proof-of-stake blocks as a stake or in proof-of-work blocks in transactions.

So you can mine proof-of-work blocks which include double-spend transactions and aim to do a reorg. You can easily check whether it's currently possible and how much of an opportunity do you lose in terms of interest and power spent on hashing. Thus you mine only when there is a chance of profit, and on average this operation will be profitable.

Even if you own just 1% of hashing power you have a chance of double-spend once in 100 blocks, which is significant.

Your ppcoin.conf file should look like this:

rpcuser = anyusernameyoulike
rpcpassword = anypasswordulike
server = 1
rpcallowip = 127.0.0.1


Then start your cgminer and add a pool:
URL: http://127.0.0.1:9902
username: same as set above for rpcuser
password: same as set above for rpcpassword

Whoever help me figure out how to get this running, I'll send them a free steam activation key for supreme commander and forged Alliance.

I installed the client and can created my ppcoin.conf file in my roaming/ppcoin folder. I'm pretty sure the ppcoin.conf file is setup wrong and that's why it can't connect or start mining. My 7950's are remaining idle.

I was unaware of that 30 day number.  It looks like it is advantageous to hoard coins without moving them between addresses.

I only have a very vague idea of what this field is really about. A quick glance at the code suggests that it shows the amount you've mined with proof of stake blocks that haven't matured yet. This is obviously still zero for everyone because proof of stake blocks require coins that have aged for at least 30 days.

Assuming your hashrate is about 700 MH/s, you should find a block every 3.8 hours on average at the current difficulty. So 6 hours is well within range.
ppcoind can't tell what your hashrate of external miners is, the gethashespersec RPC call refers to its integrated CPU miner IIUC.

I've mined a bunch of these.  My "stake" is still 0.0.  How do i get stake?  Can I use stake to get mining rewards or transaction fees?

something is wrong? i get 0 when i give "ppcoind gethashespersec"
but i use guiminer with phoenix and i see normal
hashrates in it from my 5970!
6 hours and no block yet!

Some random notes from a quick look at the source code: (I might have missed something though)

• I can't find any code path that actually mines proof of stake blocks. The code seems to be implemented, but nothing seems to be calling it yet. Proof of stake blocks definitely aren't mined through getwork, but rather through (currently inactive, or maybe I'm just blind) CPU mining.
• The difficulty for work and stake blocks seems to be (mostly?) the same, but it's divided by the number of accumulated coin days for stake blocks.
• The block reward for a work block is sqrt(sqrt(9999^4 / difficulty)), rounded down to the next cent boundary.
• The block reward for a stake block is the number of coin years put into it divided by 100.
• The number of "bruteforce attempts" for stake blocks is limited to once per second (up to 2 hours into the past), per transaction used as stake input, per block found on the network.
• Proof of stake blocks can include stake from multiple transactions, as long as it's on the same address (IIUC).
• Minimum age for coins used in a stake block is 30 days.

Sunny might want to confirm if the above is correct...

You're right. Block 1 started with difficulty of 256. Block 0 was at difficulty 1 and generated 9999 coins, but not sure if those are spendable.

That is obviously wrong. The block reward started at 2500, the difficulty at 256. A block reward of 9999 corresponds to difficulty 1.

Is that almost 7 bitcoins?!

Got to love the fact it starts at "over 9000"

Wait, does this post imply that you are trying to hold back information about how this is actually implemented, and instead want to serve the people backing your project with that kind of vague "don't worry" response?
Not very trustworthy at all... Why not answer my questions with six simple yes/no responses? I'm a bit worried now...

That's reasonably close to our expectations, we do expect some level of double-spending protection if checkpoint is not there. How strong that protection is we shall see. The current checkpoint policy leaves up to 4 hours window for folks to try mounting double-spending attacks, although this test is probably a couple months away. If you cannot tolerate any slightest double-spending risks please do wait for the checkpoint.

I'm interested to find out more about this coin. Looking at the code, it seems like Sunny has indeed been working on this since November of last year. So it's unfortunate that he decided to do kind of a rush launch of the coin. The information about how a coin works should really be announced and analyzed by the community before the blockchain is started. Now miners have to decide whether they want to jump in without knowing what they are really supporting or wait until more information is released. Couple this with the fact that the block generation starts at 9999 and decreases as difficulty increases, this coin might turn out to have a larger effective premine than SolidCoin.

I'm not convinced of that. True, they didn't release much information on this, but to me it looks like you only have the chance to use your stake to mine a block once in a blue moon. The more stake you have, the more often this will be possible, but it will still require quite a bit of luck to pull this off successfully.

Sunny, can you clarify which of the following points are correct?

• Proof of stake blocks are automatically mined by ppcoind, without an attached getwork miner.
• Proof of stake blocks are always based on a single transaction output, not multiple ones accumulated.
• Proof of stake blocks require to meet a certain difficulty target with essentially sha256(sha256(txnoutput + timestamp)).
• The timestamp used in the above calculation is checked to be within some bounds around the current network time.
• The proof of stake difficulty target is independent of the proof of work difficulty.
• The proof of stake difficulty target is calculated based on bitcoin days of the provided stake to basically pay a 1% annual interest for the time that ppcoind is running.

If all of the above are true, I think it's fairly resistant to double spends, even without checkpointing. I think central checkpointing is mostly intended to prevent proof of work based attacks in this early phase (with just about 30-50GH/s total network hashrate right now).